Page:Popular Science Monthly Volume 62.djvu/81

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weight at all times automatically occupies a similar position on the other arm. The latitude of the operations of the apparatus is further broadened by reason of the fact that the entire crane travels by its own power up and down the track or trestle on which it is mounted. A crane of this type is capable of marvelous speed. A load of fourteen tons may be hoisted at a speed of 200 feet a minute; the trolley travels back and forth along the cantilever arms at a speed of 600 feet a minute; and the entire crane has sufficient propulsive power to enable a speed of 750 feet a minute in traversing the track or trestle.

In conclusion attention must be given to the so-called lifting magnet, the most wonderful of all the new appliances for handling weighty raw material. The electro-magnet, by the aid of electricity, performs on a large scale something of the same function as the toy with which children have long been familiar. One magnet will elevate a mass of metal weighing two tons and it is possible to use several magnets simultaneously in handling a particularly heavy steel plate or bar. This plan of handling material also possesses immense economic advantages, inasmuch as a single mechanic is usually in charge of the crane to which the magnets are attached.